Sound-detecting apparatus



Sept. 1, 1925. I 1,551,821

G. A. GRAHAM Patented Sept. l 1925.

' UNITED STATES PATENT OFFICE.

GEORGE A. GRAHAM, .OF BALTIMORE, MARYLAND.

SOUND- -DETECTING APPARATUS.

. J Application filed March 21, 1925. Serial" No. 17,272.

To all whom it may concern.

Be it known that I, GEO GE A. GRAHAM, a citizen of the United States, residing at Baltimore, county .of Baltimore, State of Maryland, have invented certain new and useful Improvements in Sound-Detecting Apparatus, of which the following is a specification.

Thisinvention relates to certain improvements in acoustical apparatus whereby A acoustic phenomena developed therein may be more readily and accurately analyzed by electrical and photographic means.

The object of this invention is to provide a resonator of the most efficient volume, contour, and inlet and outlet apertures for sound waves". Another object is to provide a diaphragm within the resonator su ject to vibration upon the impact of sound waves, and to mount an electrical contact carbon button on said diaphragm in such a manner,

with respect thereto, that a minimum opposition of inertia will be imposed at the primary impulse in order to obtain a more Fig. 3 is a detail view in longitudinal sec-- tion of the inlet aperture plug.

Fig. 4 is a front end view of the resonator. Referring more particularly to the drawings, the main resonator casing- 6 is provided with threads to receive a rear or outlet head 4 and an internal shoulder 10 for the. head to abut against. The casing 6 is also provided with threads to receive a front or inlet head assembly 3 which abuts against an internal shoulder 11 of the casing. The head 1 is provided with a threaded aperture to turbances received in the casing.

A screw member 13 is screwed into the front head to retain the corrugated periphery 2' of the conical diaphragm 2 therebetween.

A metallic cap 27 with an insulating member 28 is screwed onto the head 3 which latter has an inturned collar 18 to retain a support 19 held in place by a screw cap 20. A carbon button assembly including the main body 1 has one of its component parts 14 mounted in the support 19. A sliding member 15 has a diaphragm retaining member 16 held in place by means of a nut 17. Terminals 21 and 23 are mounted in the in sulating member 28. Lead 22 connects 1'1 with 21 and lead 26 connects 21 with the binding post 9. Lead 24 connects 19 and 23 and lead 25 connects 23 with a binding post 8. A handle, of any suitable type for carrying the device, is shown at 29.

In this resonator access is only had to the outer air in two places, one hole 7 in the front head 3 and one hole 5 in the rear head 4. The hole 7 in the front head is known as the inlet aperture and is shown in detail at 7, Fig. 2, in studded form. The construction of this stud is shown in Fig. 3. The hole -in the rear head is known as the damp-' ing aperture, it is shown in detail 5 of F ig. 1. The diameter of the damping aperture is very small and of long length in comparison to the diameter of the inlet aperture. It

' will, therefore, be seenthat as a resonator,

the energy of a sound pulse acts through the inlet aperture 7' the damping aperture 5' simply acting as its name implies to dampen out sustained oscillations in the resonator.

Inthis resonator and as close as practicable to the inlet aperture a thin metal (aluminum) diaphragm is mounted as shown in detail 2, Figures 1 and 2. The diaphragm is of conical central section with corrugated periphery.

- A carbon button, detail 1, Figures 1 and 2, is securely mounted in the resonator head and attached to the diaphragm in the reverse manner to that of telephone transmitter practice. An electrical connection is made from the carbonbutton electrodes to the'binding posts details 8 and 9 of Figure 1.

Sucha resonator may, therefore, be used as an electrical method of investigating sound phenomena by electrical connection into any of the well known oscillographs. The natural frequency of such a resonator may be determined at will by simply using the desired inlet aperture stud Fig. 3, it

being an established equation in acoustics carbon button with respect to the diaphragm in a-resonator foranalysis or recording of -sound phenomena. The virtue of this manner of mounting is .to obtain a more true representation of a sound disturbance than lnprevious devices at the instlgation of the disturbance. The theory is that the manner of mounting the button is such to impose a minimum opposition of inertia, at the start of the impulse.

Consider at the very start of an impulsive sound wave when the energy component is low; in all other manners of mounting the button a considerable portion of this initial energy is consumed in overcoming the button 1nert1a itself as to change the resistance 7 of the button the granules are usually compressed on the first quarter cycle. In the reverse manner of mounting, as shown on the sketch, the inertia for this first half cycle is at a minimum.

It is 'felt that those having recourse to such instruments will appreciate the advantages and manifold applications in the physical laboratory, rad1o, telephone, or telegraph arts, for the recording of musical sounds, and the measurements of impulsive sounds of explosions, guns, etc., and the application of the present device in such calculations without the necessity of going into details in this instance.

The invention lies in the construction of an acoustical selective resonator made selective to a given fundamental frequency at will by variation of either aperture or volume. In

, this resonator and as close behind the aperture as practicable is mounted a flexible,

metallic membrane, or diaphragm, of either a low or high prime frequency as desired.

It shall be understood that the space in front of the diaphragm and rear of same are acoustically tight with respect to each other. Attached to this diaphragm is a carbon button of the type generally used to transmit voice currents in telephone transmitters, or any other type of resistance varying device. This button is mounted in such a manner that upon an initial backward movement of the diaphragm due to some impul- P sive. sound or compression wave the diaphragm movement will .pull' the carbon button stud or agitator and increase the elecing the pressure upon same;

trical resistance thru the button by lower- Inasmuch as in this movement the progression is in the direction of the least opposition it is claimed that for a given amount of energy the amount consumed in overcoming mechanical inertiais less than with'othermethods of button mounting. ture the current in the electrical circuit reproduces faithfully the diaphragm movement and the sound characteristic.

I am aware thatcthere have been similar instruments which would act more or less in the same manner on sustained oscillations but the advantage claimed in this device is the low construction inertia due to the button mounting which is advantageous at the instigation of an atmospheric disturbance. The mounting of the button in the above manner more faithfully records and portrays, in connection with proper electrical and photographic recording means, the instigation and first half cycle of all impulsive sounds with a true representation of succeeding events.

I claim 1. In a sound responsive apparatus, a resonator including a casing having an inlet and an outlet aperture, said casing being adapted to be made selective to a given fundamental frequency by a variation of volume or aperture, a conical vibratory 'diaphragm mounted in said casing and directly After the initial deparbehind said inlet aperture, a 'carbon'button supported in said casing and including an r agitator attached to said diaphragm, said agitator being adapted to lessen the pressure upon the carbon granules of said button upon an initial inward movement of said diaphragm.

2. In a sound responsive apparatus, a resonator including a casing having a front and rear head fitted therein, inlet and outlet apertured screw plugs mounted respectively in said heads, said front head having mounted therein a vibratory diaphragm and a carbon button'lof the pull type, said carbon button including an agitator connected to' said diaphragm, said diaphragm being adapted, upon sound impulse from said inlet aperture, to actuate said-carbon button, suit able binding posts and contacts with leads from said carbon button to said binding osts. '1

In testimony whereof I afiix my signature. j

GEORGE A. GRAHAM 

